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Atomos
CLIL– Content Language Integrated
g
Learning
PET - Preliminaryy English
g
Test
Teacher: Mr Pierluigi Stroppa
Tutor: Mrs Angela Valentini
1
I
Investigating
ti ti atoms
t
• You should be able to:
– Describe
D
ib th
the particle
ti l th
theory off matter
tt
according to Dalton’s atom model;
– Use
U th
the B
Bohr
h model
d l and
d kknow th
the th
three b
basic
i
particles in the atom (proton, neutron, and
electron) and their charges
charges, relative masses
masses,
and locations.
– Compare the Bohr atomic model to the
electron cloud model
2
At
Atomos:
Atomos
: Not
N t to
t Be
B Cut
C t
Th History
The
Hi t
off Atomic
At i Theory
Th
3
ATOM
Since the atom is too
smallll to
t be
b seen even
with the most powerful
p
microscopes, scientists
rely upon models to
Even with the world’s best
help
p us to understand microscopes we cannot clearly
see the structure or behavior
the atom.
of the atom.
4
S i tifi Models
Scientific
M d l
Scientists create
models to help them
to visualize complex
properties structures
properties,
or behaviors. Since
the atom is so small
small,
scientists must gather
Indirect Evidence to
develop their models.
This is a model of a very
complex molecule made of
many different kinds of atoms.
Each colored ball represents an
atom of a different element.
5
What should a Model look like?
This is a painting of a young woman
b Pablo
by
P bl Picasso.
Pi
Does
D
it actually
t ll
look like a young woman?
Scientific models
may not always
look like the actual
j
A model is
object.
an attempt to use
familiar ideas to
describe unfamiliar
things in a visual
way.
6
Is this
h really
ll an Atom?
Many of the models that you have
seen may look like the one below. It
shows the parts and structure of the
atom. Even though we do not know
what an atom looks like, scientific
models must be based on evidence.
evidence
The model above represents
the most modern version of
the atom
atom.
(Artist drawing)
drawing
7
Can a Model be Changed?
A model can be changed as new
information is collected.
collected
From the early Greek concept to the
modern atomic theory, scientists
have built upon and modified
existing models of the atom.
8
Atomic Models
• This
Thi model
d l off the
th
atom may look
familiar to you. This is
the Bohr model. In
this model, the
nucleus is orbited by
electrons, which are
in different energy
levels.
9
The Democrito
Democrito’s
s model (400 B
B.C.)
C)
• The
Th atomic
i
model has
changed
throughout the
centuries,
starting in 400
BC, when it
looked like a
billiard ball →
10
Who are these men?
In this lesson, we’ll learn
about the men whose quests
for knowledge about the
fundamental nature of the
universe helped define our
views.
Democrito, 400 b.C.
Dalton, 1800 a.C.
Rutherford, 1911 a.C.
Niels Bohr, 1913 a.C.
Thomson, 1897 a.C.
11
Democritus
• This is the Greek
philosopher
hil
h D
Democritus
it
who began the search for a
description of matter more
than 2400 years ago.
– He asked: Could matter
be divided into smaller
and smaller pieces
forever, or was there a
limit to the number of
times a piece of matter
could be divided?
divided?
400 BC
12
Atomos
• His theory: Matter could
not be divided into
smaller and smaller
pieces forever, eventually
the smallest possible
piece would be obtained.
• This piece would be
indivisible.
• He named the smallest
piece of matter “atomos,”
atomos,
meaning “not to be cut.” 13
Atomos
ƒ To Democritus, atoms
were small
small,, hard
particles that were all
made of the same
material but were
different shapes and
sizes.
ƒ Atoms were infinite in
number, always
moving and capable
of joining together. 14
D
Democritus
it
was ignored!
This theory was ignored and
f
forgotten
for
f more than
h 2000
years!
ears!
15
Why?
• The eminent
philosophers of
the time,
Aristotle and
Plato, had a
more respected,
respected
(and ultimately
wrong)) theory.
wrong
theory
Aristotle and Plato favored the earth, fire, air
and water approach to the nature of matter.
16
17
Dalton’s
Dalton s Model
• In the early 1800s,
the English
g
Chemist John
Dalton performed a
number of
experiments that
eventually led to
the acceptance of
the idea of atoms.
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Dalton’s
Dalton s Theory
• He deduced that all
elements are composed of
atoms Atoms are
atoms.
indivisible and
indestructible particles.
p
• Atoms of the same element
are exactly alike.
• Atoms of different elements
are different.
different.
• Compounds are formed by
the joining of atoms of two
or more elements.
l
t
19
Glucose
Oxygen
Carbonio
Hydrogen
20
Thomson’s Plum Pudding
Model
• In 1897,
1897, the
English scientist
J.J. Thomson
provided
id d th
the fi
firstt
hintt that
t at an
a atom
ato
is made of even
smaller particles.
particles
21
Thomson Model
• He
H proposed
da
model of the atom
that is sometimes
called the “Plum
“Plum
Pudding”” model.
Pudding
model
• Atoms were made
from a positively
charged substance
with negatively
charged electrons
scattered about, like
raisins in a pudding.
22
Thomson Model
• Thomson
Th
studied
t di d
the passage of an
electric
l t i currentt
through a gas.
• As the current
passed tthrough
oug
the gas, it gave off
rays of negatively
charged particles.
23
Thomson Model
• This surprised
Thomson
Thomson,
because the
atoms
t
off the
th gas
were
eeu
uncharged.
c a ged
Where had the
negati e charges
negative
come from?
Where did
they come
from?
24
Thomson concluded that the
negative charges came from within
the atom.
A particle smaller than an atom had
to exist.
The atom was divisible!
Thomson called the negatively
g
y
charged “corpuscles,” today known
as electrons.
Since the gas was known to be
neutral, having no charge, he
reasoned that there must be
positively charged particles in the
atom.
But he could never find them.
25
Rutherford’s Gold Foil
Experiment
• In 1908, the
English
g
p
physicist
y
Ernest Rutherford
was hard at work
on an experiment
that seemed to
have little to do
with unraveling the
mysteries
y
of the
atomic structure.
26
Rutherford’s
Rutherford s experiment
• Rutherford’s experiment Involved
firing a stream of tiny positively
charged particles at a thin sheet of
gold
ld ffoilil (2000 atoms
t
thi
thick)
k)
27
Rutherford’s
Rutherford s experiment
– Most
M t off the
th positively
iti l
charged “bullets” passed
right through the gold
atoms in the sheet of gold
foil without changing
course att all.
ll
– Some of the positively
charged “bullets
bullets,”
however, did bounce
awayy from the g
gold sheet
as if they had hit
something solid
solid.. He knew
that positive charges repel
positive charges.
28
29
The nucleus
• This
Thi could
ld only
l mean th
thatt th
the gold
ld atoms
t
iin th
the
sheet were mostly open space
space.. Atoms were not
a pudding filled with a positively charged
material.
• Rutherford concluded that an atom had a small,
small
dense, positively charged center that repelled
his positively charged “bullets
bullets.”
• He called the center of the atom the “nucleus
“nucleus””
• The nucleus is tiny compared to the atom as a
whole.
30
Rutherford
• Rutherford reasoned
that all of an atom’s
positively charged
particles were
contained in the
nucleus. The
negatively charged
particles were
scattered outside the
nucleus around the
atom’s edge
edge..
31
Bohr Model
• In 1913, the Danish
scientist Niels Bohr
proposed
p
p
an
improvement. In his
model he placed
model,
each electron in a
specific energy
level.
level
32
Bohr Model
• According
g to
Bohr’s atomic
model,, electrons
move in definite
orbits around the
nucleus, much like
planets circle the
sun. These orbits,
or energy levels
levels,,
are located at
certain distances
from the nucleus. 33
Wave Model
34
The Wave Model
• Today’s
T d ’ atomic
t i
model is based on
the principles of
wave mechanics
mechanics..
• According to the
theory of wave
mechanics,
mechanics
electrons do not
move about an
atom in a definite
path, like the
p
planets around the35
sun.
The Wave Model
• In
I fact,
f t it is
i impossible
i
ibl to
t determine
d t
i th
the exactt
location of an electron. The probable location of
an electron is based on how much energy the
electron has.
• According to the modern atomic model,
model at atom
has a small positively charged nucleus
surrounded by a large region in which there are
enough electrons to make an atom neutral.
36
Electron Cloud:
• A space in which
electrons are likely to be
found.
• Electrons whirl about the
nucleus billions of times
in one second
• They are not moving
around in random
patterns.
patterns
• Location of electrons
depends upon how much
energy the
th electron
l t
has.
h
37
Electron Cloud:
• Depending on their energy they are locked into a
certain area in the cloud
cloud.
• Electrons with the lowest energy are found in
the energy level closest to the nucleus
• Electrons with the highest energy are found
in the outermost energy levels, farther from
the nucleus.
38
Indivisible Electron
Greek
X
Dalton
X
Nucleus
Thomson
X
Rutherford
X
X
Bohr
X
X
Wave
X
X
Orbit
Electron
Cloud
X
X
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